Polymorphic form of atorvastatin calcium

ABSTRACT

The present invention relates to atorvastatin calcium, a useful agent for lowering serum cholesterol levels. New atorvastatin calcium Form V, processes for preparing the new form, and pharmaceutical compositions and dosage forms containing the new form are disclosed.

FIELD OF THE INVENTION

The present invention relates to a novel crystalline form ofatorvastatin calcium, to processes for preparing it and topharmaceutical compositions and dosages containing it.

BACKGROUND OF THE INVENTION

Atorvastatin is a member of the class of drugs called statins. Statindrugs are currently the most therapeutically effective drugs availablefor reducing low density lipoprotein (LDL) particle concentration in theblood stream of patients at risk for cardiovascular disease. A highlevel of LDL in the bloodstream has been linked to the formation ofcoronary lesions which obstruct the flow of blood and can rupture andpromote thrombosis. Goodman and Gilman, The Pharmacological Basis ofTherapeutics 879 (9th ed. 1996). Reducing plasma LDL levels has beenshown to reduce the risk of clinical events in patients withcardiovascular disease and patients who are free of cardiovasculardisease but who have hypercholesterolemia. Scandinavian SimvastatinSurvival Study Group, 1994; Lipid Research Clinics Program, 1984a,1984b.

The mechanism of action of statin drugs has been elucidated in somedetail. They interfere with the synthesis of cholesterol and othersterols in the liver by competitively inhibiting the3-hydroxy-3-methyl-glutaryl-coenzyme A reductase enzyme (“HMG-CoAreductase”). HMG-CoA reductase catalyzes the conversion HMG tomevalonate, which is the rate determining step in the biosynthesis ofcholesterol, and so, its inhibition leads to a reduction in theconcentration of cholesterol in the liver. Very low density lipoprotein(VLDL) is the biological vehicle for transporting cholesterol andtriglycerides from the liver to peripheral cells. VLDL is catabolized inthe peripheral cells which releases fatty acids which may be stored inadipocytes or oxidized by muscle. The VLDL is converted to intermediatedensity lipoprotein (IDL), which is either removed by an LDL receptor,or is converted to LDL. Decreased production of cholesterol leads to anincrease in the number of LDL receptors and corresponding reduction inthe production of LDL particles by metabolism of IDL.

Atorvastatin is the common chemical name of [R—(R*,R*)]-2-(4-fluorophenyl)-β,δ-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenylamino)carbonyl]-1H-pyrrole-1-heptanoicacid. The free acid is prone to lactonization. The molecular structureof the lactone is represented by formula (I).

Atorvastatin is marketed as the hemi calcium salt-trihydrate under thename LIPITOR by Warner-Lambert Co.

Atorvastatin was first disclosed to the public and claimed in U.S. Pat.No. 4,681,893. The hemi calcium salt depicted in formula (II) (hereafter“atorvastatin calcium”) is disclosed in U.S. Pat. No. 5,273,995. Thispatent teaches that the calcium salt is obtained by crystallization froma brine solution resulting from the transposition of the sodium saltwith CaCl₂ and further purified by recrystallization from a 5:3 mixtureof ethyl acetate and hexane. Both of these U.S. patents are herebyincorporated by reference.

The present invention includes a new crystal form of atorvastatincalcium in both hydrate and anhydrate states. Polymorphism is theproperty of some molecules and molecular complexes to assume more thanone crystalline or amorphous form in the solid state. A single molecule,like the atorvastatin in formula (I) or the salt complex of formula(II); may give rise to a variety of solids having distinct physicalproperties like solubility, X-ray diffraction pattern and solid state¹³C NMR spectrum. The differences in the physical properties ofpolymorphs result from the orientation and intermolecular interactionsof adjacent molecules (complexes) in the bulk solid. Accordingly,polymorphs are distinct solids sharing the same molecular formula, whichmay be thought of as analogous to a unit cell in metallurgy, yet havingdistinct advantageous and/or disadvantageous physical propertiescompared to other forms in the polymorph family. One of the mostimportant physical properties of pharmaceutical polymorphs is theirsolubility in aqueous solution, particularly their solubility in thegastric juices of a patient. For example, where absorption through thegastrointestinal tract is slow, it is often desirable for a drug that isunstable to conditions in the patient's stomach or intestine to dissolveslowly so that it does not accumulate in a deleterious environment. Onthe other hand, where the effectiveness of a drug correlates with peakbloodstream levels of the drug, a property shared by statin drugs, andprovided the drug is rapidly absorbed by the GI system, then a morerapidly dissolving form is likely to exhibit increased effectivenessover a comparable amount of a more slowly dissolving form.

U.S. Pat. No. 5,969,156 discloses three polymorphs of atorvastatindesignated Forms I, II, and IV by the inventors of those forms. Whilethe inventors of U.S. Pat. No. 5,969,156 claim certain processing andtherapeutic advantages of their forms over amorphous atorvastatincalcium, advantages may yet be realized by other heretofore undiscoveredforms of atorvastatin calcium.

SUMMARY OF THE INVENTION

The present invention provides new Form V of atorvastatin calcium inboth anhydrate and hydrate states, which possesses the advantage ofhigher solubility in water than atorvastatin Form I. The presentinvention further provides a process for preparing new Form V as well aspharmaceutical compositions and dosages containing the new form.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray powder diffractogram of atorvastatin calcium Form V.

FIG. 2 is a solid state ¹³C NMR spectrum of atorvastatin calcium Form V.

DETAILED DESCRIPTION OF THE INVENTION

The new crystalline form of atorvastatin calcium Form V is welldistinguished from the crystal modifications obtained by carrying outthe procedures described in U.S. Pat. Nos. 5,273,995 and 5,969,156 usingX-ray powder diffraction and solid-state ¹³C nuclear magnetic resonancetechniques.

The X-ray powder diffractogram of Form V (FIG. 1) has two medium peaksat 5.3±0.2 and 8.3±0.2 degrees 2θ and one large peak in the range 18-23degrees 2θ with a maximum at about 18.3±0.2 degrees two-theta. ThisX-Ray pattern is well distinguished from that of known Forms I, II, IIIand IV and also is well distinguished from the X-Ray pattern ofamorphous atorvastatin calcium which is characterized by two broad humpsin the ranges 8-14 degrees 2θ and 15-26 degrees 2θ. The X-ray powderdiffractogram of FIG. 1 was obtained by methods known in the art using aPhilips X-ray powder diffractometer with a curved graphite monochromatorusing goniometer model 1050/70. Copper radiation of λ=1.5418 Å was used.Measurement range: 3-30 degrees 2θ.

The solid-state ¹³C NMR spectrum of Form V is characterized by thefollowing chemical shifts:

δ (ppm) 21.9 25.9 40.4 41.8 42.3 63-73 (two broad peaks) 115.6 118.9122.5 128.7 (strong) 135.1 161.0 167.1 176-186 (broad peak)

This solid-state ¹³C NMR spectrum (FIG. 2) is well distinguished fromthose of known Forms I, II, III and IV, and also is distinguished fromthat of the amorphous form which displays a different pattern withshifts significantly different from that of Form V at 21.0 ppm, 26.4ppm, one broad peak in the range 60-75 ppm with a maximum at 69.7 ppmand 138.8 ppm. The spectrum of FIG. 2 was obtained on a Bruker DMX-500digital F NMR spectrometer operating at 125.76 MHz. The instrument wasequipped with a BL-4 cpmas probehead and a high resolution/highperformance (HPHP) ¹H for solids. The magic angle and proton decouplingefficiency were optimized before acquisition. The sample was spun at 5.0kHz spin rate on 4 mm zirconia rotors.

Atorvastatin calcium Form V may contain up to 12% water, whichcorresponds to the stoichiometric value of 9 water molecules permolecule of atorvastatin calcium. Thus, atorvastatin calcium Form V canbe in various states of hydration, between 0 and 9 moles of water.

The present invention further provides a process for the preparation ofatorvastatin calcium Form V. The process comprises the steps ofdissolving a salt of atorvastatin in a solvent to form an atorvastatinsalt solution, optionally removing impurities from the atorvastatin saltsolution, contacting the atorvastatin salt solution with a calcium saltand isolating atorvastatin calcium in new Form V.

The atorvastatin salt of the present invention includes alkali metalsalts, e.g. lithium, sodium, and potassium salts; alkaline-earth metalsalts such as magnesium salts; as well as ammonium and alkyl, aryl oralkaryl ammonium salts. The preferred atorvastatin salts are alkalimetal salts; most preferred is the sodium salt.

Any solvent capable of dissolving the atorvastatin salt and from whichatorvastatin calcium Form V may be isolated is a suitable solvent of theinvention. The choice of solvent will therefore depend upon theselection of the atorvastatin salt and the calcium salt. The solventshould be selected from those in which the atorvastatin salt and calciumsalt are at least sparingly soluble. By sparingly soluble is meant notsubstantially less soluble than 0.02 g/ml at 50-60° C. for theatorvastatin salt and not substantially less soluble than 0.0002 M at10-15° C. for the calcium salt.

Suitable solvents include but are not limited to hydroxylic solventslike water, alcohols and mixtures thereof, including hydroxylic solventsand hydroxylic solvent mixtures which have been made either acidic orbasic by addition of a mineral acid or base. Preferred solvents arewater, methanol, ethanol and mixtures thereof.

The calcium salt of the present invention includes organic and inorganicsalts of calcium which are capable of dissociating into Ca²⁺ and ananionic component when added to the atorvastatin salt solution. Amongthe organic salts that may be used are carboxylates and sulfonates.Among the carboxylates are lower alkyl carboxylates like acetate,proprionate, butyrate and tartrate and aryl carboxylates like benzoateand phthalate as well as higher alkyl carboxylates like stearate,dodecanoate and the like. Also included are calcium ascorbate andsuccinate. Among the sulfonates that may be used are lower alkyl andaryl sulfonates like calcium methane sulfonate, calcium benzenesulfonate and calcium p-toluene sulfonate. The preferred organic calciumsalts are lower carboxylate salts, the most preferred organic calciumsalt is calcium acetate.

Depending upon solubility, inorganic salts which may be used includehalide salts such as CaCl₂, CaF₂, CaBr₂ and CaI₂, as well as calciumborate (B₄CaO₇), calcium tetrafluoroborate (CaBF₄), calcium carbonate(CaCO₃), monobasic calcium phosphate (Ca(H₂PO₄)₂), dibasic calciumphosphate (CaHPO₄) and tribasic calcium phosphate (Ca(PO₄)₂), calciumsulfate (CaSO₄) and calcium hydroxide (Ca(OH)₂), and hydrates thereof.

Whether organic or inorganic, the calcium salt is preferably added in anamount that provides one half mole of Ca²⁺ per mole of atorvastatin inthe atorvastatin salt solution. For example, if the atorvastatin salt isatorvastatin sodium (atorvastatin⁻ Na⁺), then about one half mole ofcalcium salt per mole of the atorvastatin salt is appropriate. If theatorvastatin salt is atorvastatin magnesium ([atorvastatin⁻]₂ Mg²⁺),then about one mole of calcium salt per mole of atorvastatin salt isappropriate. Otherwise, mixed salts containing atorvastatin may form.

The calcium salt may be contacted with the atorvastatin salt solution byadding the calcium salt in substantially pure form, i.e. either as asolid or, if liquid, as a neat liquid, to the atorvastatin salt solutionor, preferably, by first forming a calcium salt solution and thencontacting the atorvastatin salt solution and calcium salt solution. Itis most preferred to contact the calcium salt and the atorvastatin saltsolution by first dissolving the calcium salt in a solvent and thenadding the calcium salt solution to the atorvastatin salt solutionslowly. Suitable calcium salt solvents are solvents previously mentionedas being suitable solvents for the atorvastatin salt, provided thecalcium salt is at least sparingly soluble in the particular solvent.

In a particularly preferred embodiment, wherein the atorvastatin salt isan atorvastatin alkali metal salt and the atorvastatin salt solvent is a1:2 methanol:water mixture, the preferred calcium salt is calciumacetate and the preferred calcium salt solvent is water. When thecalcium salt solvent is water, it is preferably used in an amount thatprovides about a 20 to 30 millimolar solution of the calcium salt, morepreferably about a 25 millimolar solution.

In addition, the atorvastatin and calcium salts are preferably combinedat elevated temperature and at concentrations disclosed above and in theexamples, which follow, in order that crystallization of Form V may beinduced by cooling of the so-formed atorvastatin calcium solution. Theelevated temperature is preferably above 40° C. and below 80° C., morepreferably above 50° C. and below 70° C. and most preferably about 60°C. One skilled in the art will appreciate that by adjusting temperatureand concentration, the yield of atorvastatin calcium Form V may beoptimized. Crystallization of atorvastatin calcium Form V may also beinduced by addition of a seed crystal of atorvastatin calcium,preferably Form V although other forms also may be used.

Once crystals of atorvastatin Form V have crystallized, eitherspontaneously, upon cooling, upon seeding or by another inducement, thecrystals may be isolated by filtration or other conventional means knownto the art. The isolated crystals may also be dried by conventionalmeans.

It has also been found that atorvastatin-calcium can be crystallized inForm V by dissolving atorvastatin calcium in THF or alcohols likemethanol or ethanol, and subsequently adding water as an antisolvent.

A further aspect of the present invention is a pharmaceuticalcomposition and dosage form containing the novel form of atorvastatincalcium.

The compositions of the invention include powders, granulates,aggregates and other solid compositions comprising novel Form V ofatorvastatin calcium. In addition, Form V solid compositions that arecontemplated by the present invention may further included diluents,such as cellulose-derived materials like powdered cellulose,microcrystalline cellulose, microfine cellulose, methyl cellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,hydroxypropylmethyl cellulose, carboxymethyl cellulose salts and othersubstituted and unsubstituted celluloses; starch; pregelatinized starch;inorganic diluents like calcium carbonate and calcium diphosphate andother diluents known to the pharmaceutical industry. Yet other suitablediluents include waxes, sugars and sugar alcohols like mannitol andsorbitol, acrylate polymers and copolymers, as well as pectin, dextrinand gelatin.

Further excipients that are within the contemplation of the presentinvention include binders, such as acacia gum, pregelatinized starch,sodium alginate, glucose and other binders used in wet and drygranulation and direct compression tableting processes. Excipients thatmay also be present in a solid composition of Form V atorvastatincalcium further include disintegrants like sodium-starch glycolate,crospovidone, low-substituted hydroxypropyl cellulose and others. Inaddition, excipients may include tableting lubricants like magnesium andcalcium stearate and sodium stearyl fumarate; flavorings; sweeteners;preservatives; pharmaceutically acceptable dyes and glidants such assilicon dioxide.

The dosages include dosages suitable for oral, buccal, rectal,parenteral (including subcutaneous, intramuscular, and intravenous),inhalant and ophthalmic administration. Although the most suitable routein any given case will depend on the nature and severity of thecondition being treated, the most preferred route of the presentinvention is oral. The Dosages may be conveniently presented in unitdosage form and prepared by any of the methods well-known in the art ofpharmacy.

Dosage forms include solid dosage forms, like tablets, powders,capsules, suppositories, sachets, troches and losenges as well as liquidsuspensions and elixirs. While the description is not intended to belimiting, the invention is also not intended to pertain to truesolutions of atorvastatin calcium whereupon the properties thatdistinguish the solid forms of atorvastatin calcium are lost. However,the use of the novel forms to prepare such solutions (e.g. so as todeliver, in addition to atorvastatin, a solvate to said solution in acertain ratio with a solvate) is considered to be within thecontemplated invention.

Capsule dosages, of course, will contain the solid composition within acapsule which may be made of gelatin or other conventional encapsulatingmaterial. Tablets and powders may be coated. Tablets and powders may becoated with an enteric coating. The enteric coated powder forms may havecoatings comprising phthalic acid cellulose acetate,hydroxypropylmethyl-cellulose phthalate, polyvinyl alcohol phthalate,carboxymethylethylcellulose, a copolymer of styrene and maleic acid, acopolymer of methacrylic acid and methyl methacrylate, and likematerials, and if desired, they may be employed with suitableplasticizers and/or extending agents. A coated tablet may have a coatingon the surface of the tablet or may be a tablet comprising a powder orgranules with an enteric-coating.

Preferred unit dosages of the pharmaceutical compositions of thisinvention typically contain from 0.5 to 100 mg of the novel atorvastatincalcium Form V, or mixtures thereof with other forms of atorvastatincalcium. More usually, the combined weight of the atorvastatin calciumforms of a unit dosage are from 2.5 mg. to 80 mg.

Having thus described the various aspects of the present invention, thefollowing examples are provided to illustrate specific embodiments ofthe present invention. They are not intended to be limiting in any way.

EXAMPLES Example 1

The sodium salt of atorvastatin (52.2 g) was dissolved in methanol (510ml) and then diluted with water (1 L). The resulting solution wastransferred to a separatory funnel containing 1:1 ethyl acetate/hexane(1 L). The phases were mixed by bubbling nitrogen gas through theseparatory funnel. Upon cessation of nitrogen flow, the phases separatedand the upper, organic, phase was removed. The lower, aqueous, phase waswashed with 1:1 ethyl acetate/hexane (1 L) and then transferred to around bottom flask. Active charcoal (10.2 g) was added. The flask washeated to 50° C. and the solution was stirred for two hours. Theactivated charcoal was then removed by filtration through celite, thecharcoal and celite being rinsed with methanol (1540 ml), and therinsate and filtrate then being combined into one atorvastatin sodiumsalt solution.

The quantity of atorvastatin obtained by purification was determined bycalibrated HPLC analysis of the purified atorvastatin sodium saltsolution. Based on this analysis, a quantity of calcium acetate (8.38 g,0.5 eq.) was dissolved in water (1.9 L) and heated to 60° C. Theatorvastatin sodium salt solution was heated to 63° C. and the solutionswere combined by slow addition of the calcium acetate solution to theatorvastatin sodium salt solution. Upon completing the addition, themixture was cooled. Crystallization of Form V began to occur at atemperature of 43° C. and cooling was continued until the flasktemperature reached 13° C.

The crystals were isolated by slow vacuum filtration and then dried overanhydrous silica for 5 days to yield atorvastatin calcium salt Form V.

Example 2

Atorvastatin calcium (10 g) was dissolved in methanol (400 ml) at roomtemperature. Water (300 ml) was added slowly to the methanolic solutionwith stirring and the resulting solution was heated to 60° C. Thesolution was then cooled to between 10 and 15° C. within 3 h.Precipitation started at about 40° C. The thick slurry was then dried at50° C. under reduced pressure for 48 h to yield atorvastatin calciumForm V.

Example 3

Atorvastatin calcium (5 g) was dissolved in methanol (100 ml) at roomtemperature. To this methanolic solution, water (100 ml) was added whilestirring. Precipitation occurred instantly and after cooling the slurryto 15° C. the precipitate was filtered and dried at 50° C. under reducedpressure for 48 h to yield atorvastatin calcium Form V.

Example 4

Atorvastatin calcium (5 g) was dissolved in methanol (200 ml). Themethanolic solution was placed into a stirred reactor containing water(150 ml) at 45° C. The obtained slurry was cooled to 10° C., filteredand dried at 50° C. under reduced pressure for 48 h to yieldatorvastatin calcium Form V.

Example 5

Atorvastatin calcium (1 g) was dissolved in ethanol (15 ml) afterheating. To this ethanolic solution, water (10 ml) was added whilestirring. Precipitation occurred instantly. The gel-like precipitate wasfiltered without vacuum and dried at 50° C. under reduced pressure for24 h to yield atorvastatin calcium Form V.

Example 6

Atorvastatin calcium (1 g) was dissolved in THF (25 ml) at roomtemperature. To this solution, water (60 ml) was added while stirring.The reaction mixture was stirred for 18 hours at room temperature andthe precipitate (gel) was filtered without vacuum and dried at 50° C.under reduced pressure for 24 h to yield atorvastatin calcium Form V.

The invention has been described with reference to its preferredembodiments. From this description, those skilled in the art mayappreciate changes that could be made in the invention which do notdepart from the scope and spirit of the invention as described above andclaimed hereafter.

1. Atorvastatin calcium Form V having an X-ray powder diffractogramsubstantially as depicted in FIG.
 1. 2. Atorvastatin calcium Form Vcharacterized by X-ray powder diffraction peaks at 5.3±0.2 and 8.3±0.2degrees 2θ and a broad peak at 18-23±0.2 degrees 2θ with a maximum at18.3±0.2 degrees 2θ.
 3. Atorvastatin calcium Form V having a solid state¹³C NMR spectrum substantially as depicted in FIG.
 2. 4. Atorvastatincalcium Form V characterized by solid state ¹³C NMR signals at 21.9,25.9, 118.9, 122.5, 128.7, 161.0 and 167.1 ppm.
 5. Atorvastatin calciumForm V characterized by X-ray powder diffraction peaks at 5.3±0.2 and8.3±0.2 degrees 2θ and solid state ¹³C NMR signals at 21.9, 25.9, 118.9,122.5, 128.7, 161.0 and 167.1 ppm.
 6. Atorvastatin calcium Form Vaccording to any one of claims 1, 3, 4 or 5 produced by a processcomprising the steps of a) dissolving a metal, ammonium or alkylammoniumsalt of atorvastatin in a solvent to form an atorvastatin salt solution,b) contacting the atorvastatin salt solution with a calcium salt, and c)isolating atorvastatin calcium Form V.